196 INDEX TO THE STRATIGKAPHY OF NOETH AMERICA. 



The "Trenton group" is represented by gray limestones with shaly and marly 

 beds, approximately 320 feet thick. Locally these strata rest upon the Ste. Marie 

 sandstone ^*^^ or directly upon the pre-Cambrian quartzite ledges of the north- 

 eastern islands (Badgely Point, etc.), where they carry Black River fossils. Ami ^^ 

 cites a number of collections of fossils from these strata. 



"Hudson River" strata of the islands are described as bluish-gray. and drab 

 marls and shales, interstratified with thin limestone and fine-grained sandstone, 

 altogether 250 to 300 feet thick, including a 30 to 40 foot band of limestone at the 

 top. Ami states: 



It is extremely desirable that further collections be obtained from the Ordovician and 

 SUurian succession of the Manitoulin Island district of Lake Huron, inasmuch as the sedimenta- 

 tion of that area is not only quite distinct from that of the Niagara and Toronto districts on the 

 Ontario basin, but bears strong resemblance to the succession known and recorded in Indiana, 

 Ohio, and Kentucky to the south, as well as to that of the Island of Anticosti, in the valley of the 

 St. Lawrence, east. 



The beds called Utica shale are described as black and bituminous and 60 feet 

 thick. Some of the collections (Nos. 14-20) contain faunas which appear to indicate 

 the presence of the summit beds of the Ordovician, either Lorraine or Richmond; 

 elsewhere Lorraine (21-22) and Richmond (23-32) have been distinctly recognized. 

 To the Clinton (Medina strata being absent) are assigned drab, buff, and purplish 

 magnesian limestones. 



L 17. LAKE NIPISSING, LAKE TEMISCAMING, AND MATTAWA. 



Outliers of Ordovician limestone containing Black River and Trenton faunas 

 occur on islands in Lake Nipissing, Lake Temiscaming, and 6 miles below Mattawa, 

 on the Ottawa.'^ They are too small to be shown on the map but are important, 

 as their correlation, according to Ami,^'* shows " that in Ordovician times the marine 

 waters of the Lake Huron Paleozoic basin were directly connected with those of the 

 Nipissing and Mattawa or Upper Ottawa regions." 



L 18-19. ST. LAWRENCE VALIiEY. 



The distribution of the Ordovician, exclusive of the Beekmantown (" Calcifer- 

 ous"), in the St. Lawrence Valley as here mapped is taken from the map sheets of 

 Ontario and Quebec. The line at the base is that between the "Calciferous" and 

 Chazy, and that part of the Ordovician above this line comprises the equivalent of 

 the Chazy, Lowville ("Birdseye"), Black River, Trenton, Utica, and Lorraine of 

 the New York section. The Pamelia limestone ^^ and the underlying but uncon- 

 formable "Theresa formation" have also been traced in the latest work (1908)." 



The southwestern or upper part of the St. Lawrence Valley is known in Canadian 

 geology as the Ottawa Basin. This basin is bounded on the southwest by the 

 Frontenac axis, the belt of pre-Cambrian rocks which crosses the St. Lawrence and 

 connects with the Adirondack area. On the east a similar area of older rocks, 

 eroded to the Potsdam sandstone, separates the Ordovician of the Ottawa basin from 

 the equivalent Ordovician strata that extend from Montreal to Quebec, down the 

 north side of the St. Lawrence Valley. 



'Ami., H. M., personal communication, Sept., 1908. 



